P5490100 (pôr-fîr′ə-blăst′)n. A large crystal that is surrounded by a fine-grained matrix in a metamorphic rock and forms from the recrystallization of existing mineral crystals during metamorphism.[porphyr(y) + —blast.]
porphyroblast
enUK
porphyroblast
[pȯr′fir·ə‚blast] (petrology) A relatively large crystal formed in a metamorphic rock.